was it a leap of faith, or a logical deduction that he was willing to risk? Jack did seem to realize Jabob had intentions for them all on a grand scale and that anything seemingly supernatural is possible. But at the same time... the way Jack acted as the fuze neared it's end seemed more like he had faith.
the writers of this show are great about leaving things so they can be interpreted many ways. it's very irritating because you cant always draw solid conclusions, but that's what keeps me coming back week after week.